1. Field of the Invention
The invention relates to a method for detecting scratches on a film surface. More particularly, the invention relates to a method and apparatus for mapping scratches on a surface layer of a semiconductor wafer, such as an oxide film, which may occur during processing of the wafer.
2. Related Art
During the processing of semiconductor wafers, there is usually a step involving polishing or planarizing the surface of the wafer. This polishing or planarizing step often causes scratches on the wafer surface. It is important that the location, size, and depth of these scratches be identified early before they become problematic. For instance, replicated scratches can fill with residual metal in subsequent processing steps.
In the past, the inspection process was accomplished visually by a skilled person. In many instances, however, these scratches are very small and difficult to identify with the naked eye. In particular, integrated circuits have recently been excessively miniaturized in size, and surface scratches which occur could be only 1 .mu.m or less in size. Obviously, such small scratches are impossible to identify with the naked eye.
In order to overcome the inadequacies of visual inspection, methods have been developed for improved identification of scratches on a wafer surface. One method entails detecting scratches on a wafer surface by scattering light onto the wafer surface (see U.S. Pat. No. 4,626,101). Although effective in some instances, this technique inherently is not effective for defect detection on certain wafer surfaces such as oxide or nitride. Oxide and nitride are just some of the common films used as a stop layer for the polishing process of semiconductor wafers. With the use of known light scattering techniques, it is very difficult to detect scratches in oxide and nitride.
Accordingly, recent attempts have been made to better detect defects on oxide and nitride layers. For example, International Business Machines Corporation has developed a technique whereby scratch detection is based on using a highlighting wet etch process involving three wet steps to highlight the scratches (IBM Technical Disclosure Bulletin, vol. 34, No. 4B, September, 1991). The highlighting steps are followed by conventional light scattering to detect the scratches. This process is time-consuming and potentially contaminating due to the wet steps.
Therefore, there is a need for a simple and more efficient method of scratch detection on wafer surfaces, and in particular, on surface layers comprising nitride or oxide.